The invention relates to an oscillatory drive having a housing in which there are accommodated a drive motor for driving a motor shaft in rotation and a tool spindle, and a first coupling drive mechanism which is coupled to the motor shaft and to the tool spindle for the purpose of driving the tool spindle in oscillatory fashion about its longitudinal axis, and a second coupling drive mechanism which is coupled to the tool spindle.
An oscillatory drive of said type is known from EP 2 594 364 A1.
Oscillatory drives of known construction can be used for driving hand-held power tools for performing a wide variety of tasks, including in particular sawing tasks, cutting tasks and grinding tasks. Oscillatory drives are normally designed to drive a tool with a high oscillation frequency, for example in the range between 5000 oscillations per minute and 30 000 oscillations per minute (measured from reversal point to reversal point), with a small pivot angle, for example in the range between 0.5° and 7°. Highly precise machining of workpieces can be made possible in this way. During the machining of the workpieces, the tool that is driven in oscillatory fashion generates only low reaction forces or counteracting moments that must be absorbed by an operator controlling the oscillatory drive. Compared, for example, with sawing tools that are driven in rotation, for example circular saws, saw blades that are driven in oscillatory fashion pose a significantly lower risk of injury to the user. Furthermore, with elongate saw blades, it is possible for plunge cuts to be formed in particular into workpieces composed of wood, glass-fiber reinforced plastic (GRP), plaster or the like, which is possible only to a restricted extent with tools that are driven in rotation.
However, when forming plunge cuts, there is the problem that the chip spaces quickly become filled with sawdust. Furthermore, the saw blade which does not cut in a sideward direction but merely oscillates is laterally constrained during the plunge cut and is thus prevented from vibrating. The oscillation is thus relocated into the gear, into the receptacle and into the saw blade itself, and exerts load on the parts by elastic deformation and/or is converted into friction heat. In the extreme case, the saw blade comes fully to a standstill, and the machine moves back and forth.
In the case of EP 2 594 364 A1 as cited in the introduction, the oscillatory drive is provided with two eccentric coupling mechanisms, whereby it is the intention for the oscillatory movement of the tool spindle to take place with direction-dependent deflection. This means that, depending on the design of the two eccentric coupling mechanisms and depending on the switching state of the freewheels, either a conventional oscillation of the tool spindle takes place, in which it is pivoted forward and backward by the same angle in alternating fashion, or that a rotational progression can be obtained which increases in oscillatory fashion in one direction of rotation. Both cases, however, involve an oscillation about a pivot axis that is static with respect to the appliance.
The problems described above also exist in the case of an embodiment of that type.